In recent years, color copying apparatuses, which are one form of image forming apparatuses, are adapted to create a color image by converting a document, which was scanned by a solid-state imaging device of an image reading section, into image information in the form of an electrical signal, and by inputting the electrical signal into a color image forming section. The solid-state imaging device usually employs a color CCD sensor of a structure in which color filters of R, G, B (red, green, blue) are placed on a light-receiving area of the color CCD section.
The electrical signal of the image information which was obtained by scanning the document is subjected to an image process, before it is outputted from a color image processing section, to create an image in conformity with the document. That is, the image processing for controlling the electrical signal of the image information is performed to form a conform image according to input/output characteristic values of input/output means of the image reading section including the solid-state imaging device, or the color image forming section.
The input/output characteristic values of the input/output means differ depending on such factors as components making up the apparatus or a control method, and there is need to set the input/output characteristic values for each individual apparatus. This is commonly carried out by (1) a method in which a reference document is read by the image reading section to set the input/output characteristic values, and (2) a method in which an image created by the color image forming section based on an electrical signal of the image information which was obtained from the image reading section is outputted therefrom, and the output image is read again by the image reading section to set the input/output characteristic values.
However, the problem of such a conventional image forming apparatus is that it takes effort to set the input/output characteristic values. Namely, the image forming apparatus includes a number of image forming modes for different kinds of documents, such as a document including ordinary characters, a document including dot images, and a document including photographic images. This necessitated the conventional method of setting the input/output characteristic values to use different reference documents for different image forming modes and to set the input/output characteristic values individually for each reference document, thus posing the problem of troublesome setting of the input/output characteristic values.
Therefore, there are conventional problems that it takes time to set the input/output characteristic values because they are set for the number of times which corresponds to the number of image forming modes, and that, in the event where the reference document was different for each image forming mode, there were cases where a different reference document was used erroneously, which necessitated re-setting and also resulted in a prolonged operation time for setting the input/output characteristic values.